Precise and real-time identification of reservoir fluid composition are important for successful evaluation and development of oil-gas-water reservoirs. Reservoir fluid composition influences all aspects of reservoir development including well design, method to improve recovery factor, and production strategy. It is important to evaluate reservoir fluid compositions in real time, or at least near real time. Real-time analysis preferably includes evaluations within the well bore, also referred to as “downhole.” It is usually possible, although typically less timely, to evaluate extracted samples in a surface laboratory. To obtain downhole samples, a special tool is lowered into the well and set across points of interest. An example of such a tool is described in U.S. Pat. No. 5,166,747, assigned to Schlumberger Technology Corporation, the disclosure of which is incorporated herein by reference in its entirety. By establishing communication with the reservoir, the reservoir fluids are extracted, or withdrawn from the reservoir towards the tool. The extracted fluids are directed into fluid storage and fluid composition analysis modules.
Methods exist for determining fluid composition. These methods typically include a detection device capable of performing gas and liquid chromatography. Such devices can qualitatively and/or quantitatively respond to analyzable mixtures, including hydrocarbon mixtures encountered in oilfield applications. Some of the most commonly used detectors include thermal conductivity detectors, flame ionization detectors, photometric detectors, and photo ionization detectors.
Techniques exist for determining fluid composition, which inject infrared light into a flowing sample and measure a portion of the injected light to determine an amount of absorption by the sample. These techniques use optical or infrared (IR) absorption detectors to detect the difference in beam intensity before and after its passing through a sample cell, which includes a sample mixture to be analyzed. Atoms and/or molecules within the sample capture some of the photons as they traverse the sample cell through a process referred to as electron excitation—the movement of an electron within an atom or molecule of the sample to a higher energy state. Such techniques generally determine electron excitation of molecules within the sample. Unfortunately, it is often difficult and at times impossible to select wavelengths from within the optical band that will provide substance identification due to overlapping absorption peaks or emission peaks that occur within this range.